1. Field of the Invention
The present invention relates generally to weighty object mounting systems, and more particularly, is directed to improvements in a weigty object mounting system for use in an assembly line wherein a weighty object such as an engine unit is mounted on a transportable object such as a vehicle body held by a moving support member and transported into a working station provided therein.
1. Description of the Prior Art
In a vehicle assembly line wherein a weighty object such as an engine unit or a suspension unit is mounted on a vehicle body, usually, the vehicle body is supported by a hanger engaged to be movable with a tact conveyer of the overhead type ard tact-transported into a mounting station. At the mounting station, a weighty object mounting system having a lifting table movable in the vertical, longitudinal and lateral directions, as disclosed in the Japanese patent application published before examination under publication No. 59-206266, is provided and the weighty object is placed on the lifting table. On the occasion of mounting actually, the weighty object is lifted by the lifting table to move into a mounting position on the vehicle body transported into the mounting station and thereat attached to the vehicle body with a plurality of bolts or the like.
Such mounting of the weighty object on the vehicle body in the vehicle assembly line proposed previously is achieved manually by workers and it is required of each worker to have an annoying control of tightening torque affecting the bolt for causing the weighty object to be fixed to the vehicle body. Accordingly, it is desired that the mounting of the weighty object on the vehicle body is conducted by automatized mechanical work without relying upon manual labour by a worker.
However, the vehicle body transported into the mounting station is usually accompanied with misalignments arising in relation to the weighty object placed on the lifting table due to, for example, unavoidable errors in size of each vehicle body and each hanger supporting the vehicle body or errors in position of the vehicle body supported by the hanger. Therefore, in the case of the mounting of the weighty object on the vehicle body intended to be conducted by automatized mechanical work, it is feared that the weighty object lifted by the lifting table is not moved appropriately into the mounting position on the vehicle body so as not to be properly attached to the vehicle dody with the bolts tightened by the automatized mechanical work.
In order to avoid such misalignments arising between the vehicle body transported into the mounting station and the weighty object placed on the lifting table in the mounting station, it is considered to detect the location of the vehicle body supported by the hanger and transported to the working station and to shift the lifting table accompanied with the weighty object in a plane along the direction of transportation of the vehicle body in response to a detection output of the location of the vehicle body so that the position of the weighty object corresponds properly to the location of the vehicle body. However, in such a case, since the location of the vehicle body supported by the hanger may be detected by an optical position sensor provided in a positioning station which is established to be adjacent to the mounting station at the upper course of the vehicle assembly line, it is also feared that the vehicle body supported by the hanger has a slight error in position thereof arising undesirably on a transporting path from the positioning station to the mounting station. In the case where the slight positional error of the vehicle body supported by the hanger thus brought about, for example, such a situation that the bolts, each of which is to be inserted into a couple of mounting holes provided respectively on the vehicle body and the weighty object and tightened for causing the weighty object to be fixed to the vehicle body, can not be inserted into the respective holes, may occur in the mounting station, and therefore the weighty object may not be properly attached to the vehicle body, even though the lifting table accompanied with the weighty object is shifted in the plane along the direction of transportation of the vehicle body in response to the detection output of the location of the vehicle body obtained at the positioning station.